DESCRIPTION: The goal of this application is to study the role of the apterous (ap) gene in various aspects of Drosophila development. Ap encodes a homeobox protein containing a LIM domain which has been implicated in protein-protein interactions. Ap is required for a series of developmental decisions including dorso/ventral compartmentalization of the wing, fasciculation of specific interneurons in the ventral nerve cord, development of the optic lobe and determination of thoracic muscles in the embryo. Ap null mutants have very short adult life spans (1-3 days) and lack juvenile hormone, causing defects in oogenesis. Expression of the ap gene is controlled by a series of independent enhancers that mediate transcription in the various tissues where its function is required: brain, ventral nerve cord, muscle, adult tracheoblasts, ring glands, and imaginal discs. Expression of ap in the ventral nerve cord is controlled by Scr, Ant, and Ubx, and binding sites for these proteins have been found in the enhancer controlling ap transcription in this tissue. The first part of the application is an study of the role of the LIM domain in ap function. For this purpose Dr. Botas has isolated a GAL4 enhancer insertion into the ap gene that causes a null phenotype and drives expression of GAL4 in all the tissues where ap is normally expressed. This insertion can drive normal expression of a GAL4 UAS-apterous cDNA to rescue the phenotype of ap mutants. Mutations will be made in specific residues of the LIM and homeo domains and introduced into this construct. After P element transformation, the transformed strains will be crossed to the GAL4-ap enhancer trap or to strains carrying GAL4 under the control of specific enhancers of the ap gene. Preliminary results suggest that the effects of ap mutations in adult viability and female fertility are caused by lack of ap function in the tracheoblasts and corpus allatum of the ring gland respectively, although expression of ap in these tissues could not be detected with available antibodies. To address this question, Dr. Botas will prepare new monoclonal antibodies against the ap protein. These antibodies will be used to investigate whether ap is expressed in these tissues, supporting a role for the ap gene in juvenile hormone production and the morphogenesis of the respiratory system. These antibodies will also be used to study the expression of ap in the optic lobes during pupal and adult development, since mutations in ap show a severe disorganization of the lobula complex neuropil possibly due to defects in axon guidance similar to those observed in the ventral nerve cord during embryonic development. Specific cells that show the mutant phenotype will be identified using the ap-GAL4 enhancer line to drive expression of a tau-GFP reporter gene.